Some mechanical devices perform specific functions through use of induced vibratory motion. Such devices include may be used to provide services such as monitoring damage detection and structural assessment of civil structures and mechanical devices, damping in civil structures, searching for oil and gas with seismic impulse exciters, and medical devices. Such devices may also include equipment for controlling fluid flow in a pipe, deliquifying screens, and equipment that functions as material separators, vibratory feeders and conveyors, attrition mills, mold shakeout machines, and vibratory compactors. Typically, these devices utilize one or more force generators to create a predefined force profile suitable for inducing a desired vibration within the device. These force generators may include linear drives or imbalanced rotors driven by synchronous motors or induction motors whose speed is an integer fraction of the electrical source frequency. To vary the frequency of vibration, variable frequency drives (VFDs) are used in conjunction with these motors. To tailor the shape of the vibration profile or create a resonance for the purpose of amplifying the vibration response, springs, stabilizers, and/or mechanical pivots are used. When multiple synchronous or asynchronous motors are used on the same device and are coupled through common base vibration, they tend to synchronize with each other to produce a consistent and predesigned force profile.
The aforementioned devices are incapable of maintaining a desired vibration profile for the mechanical device when operating conditions change (e.g., changes in material loading, changes in temperature, changes in material properties, or other variables that can alter the response of the mechanical device). In some cases, the aforementioned devices cannot create certain desirable vibration profiles. In other cases, the aforementioned devices cannot create a variety of selectable vibration profiles within limits imposed by the authority of their respective force generators.